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#+title: AMS review of 'Double Macdonald polynomials as the stable limit
#+title: of Macdonald superpolynomials' by Blondeau-Fournier, Lapointe and
#+title: Mathieu

#+date: <2015-07-15>

A Macdonald superpolynomial (introduced in [O. Blondeau-Fournier et al.,
Lett. Math. Phys. 101 (2012), no. 1, 27--47;
[[http://www.ams.org/mathscinet/search/publdoc.html?pg1=MR&s1=2935476&loc=fromrevtext][MR2935476]];
J. Comb. 3 (2012), no. 3, 495--561;
[[http://www.ams.org/mathscinet/search/publdoc.html?pg1=MR&s1=3029444&loc=fromrevtext][MR3029444]]])
in \(N\) Grassmannian variables indexed by a superpartition \(\Lambda\)
is said to be stable if \({m (m + 1) \over 2} \ge |\Lambda|\) and \(N
\ge |\Lambda| - {m (m - 3) \over 2}\) , where \(m\) is the fermionic
degree. A stable Macdonald superpolynomial (corresponding to a
bisymmetric polynomial) is also called a double Macdonald polynomial
(dMp). The main result of this paper is the factorisation of a dMp into
plethysms of two classical Macdonald polynomials (Theorem 5). Based on
this result, this paper

1) shows that the dMp has a unique decomposition into bisymmetric
   monomials;

2) calculates the norm of the dMp;

3) calculates the kernel of the Cauchy-Littlewood-type identity of the
   dMp;

4) shows the specialisation of the aforementioned factorisation to the
   Jack, Hall-Littlewood and Schur cases. One of the three Schur
   specialisations, denoted as \(s_{\lambda, \mu}\), also appears in (7)
   and (9) below;

5) defines the \(\omega\) -automorphism in this setting, which was used
   to prove an identity involving products of four Littlewood-Richardson
   coefficients;

6) shows an explicit evaluation of the dMp motivated by the most general
   evaluation of the usual Macdonald polynomials;

7) relates dMps with the representation theory of the hyperoctahedral
   group \(B_n\) via the double Kostka coefficients (which are defined
   as the entries of the transition matrix from the bisymmetric Schur
   functions \(s_{\lambda, \mu}\) to the modified dMps);

8) shows that the double Kostka coefficients have the positivity and the
   symmetry property, and can be written as sums of products of the
   usual Kostka coefficients;

9) defines an operator \(\nabla^B\) as an analogue of the nabla operator
   \(\nabla\) introduced in [F. Bergeron and A. M. Garsia, in /Algebraic
   methods and \(q\)-special functions/ (Montréal, QC, 1996), 1--52, CRM
   Proc. Lecture Notes, 22, Amer. Math. Soc., Providence, RI, 1999;
   [[http://www.ams.org/mathscinet/search/publdoc.html?r=1&pg1=MR&s1=1726826&loc=fromrevtext][MR1726826]]].
   The action of \(\nabla^B\) on the bisymmetric Schur function
   \(s_{\lambda, \mu}\) yields the dimension formula \((h + 1)^r\) for
   the corresponding representation of \(B_n\) , where \(h\) and \(r\)
   are the Coxeter number and the rank of \(B_n\) , in the same way that
   the action of \(\nabla\) on the \(n\) th elementary symmetric
   function leads to the same formula for the group of type \(A_n\) .

Copyright notice: This review is published at
http://www.ams.org/mathscinet-getitem?mr=3306078, its copyright owned by
the AMS.
